AstroPlanck - Learn About Stars' Light and Color

The program is an interactive demonstration of spectral radiation laws, including Planck's Law, Wien's Law, Stephan-Boltzmann's Law and luminosity as a function of size and temperature. It shows how these important radiation laws behave as related to our observations of stars and in understanding the meaning of the cosmic background radiation. These radiation laws deal with energy output as a function of how hot an object, like a star, is.

Temperature values for stars range from about 1000 K to 100,000 K. By inputting a stellar temperature you can see how the star emits lights in different parts of the energy spectrum. You may plot up to eight curves at one time and see vividly the part of their energy output visible to the human eye and how star colors result from their temperatures.

Another program feature is the list of notable stars to compare with our Sun. Star outputs are displayed on the Planck spectrum diagram. Another screen displays disks representing the star and Sun, comparing size, color, and intensity. To supplement the list, you may enter values of size and temperature, making your own star to compare with the Sun.

Max Planck had quite a problem in modern physics to wrestle with. Insight into the way light is emitted by hot objects was being gained by studies in the lab of the spectral output of spherical cavities painted black, but glowing hot. A black body looks black only so long as it is cool enough to absorb light at visible wavelengths. If it gets hot enough, its radiated light will be visible and may appear quite bright in fact, with any color of the rainbow.

Planck discovered that on the smallest of scales, energy states exist at discrete levels or quanta, not in a continuous spectrum of levels. This helped explain the spectra of objects like stars and helped lead the way to develop quantum physics.

Wien's Law predicts at what wavelength the intensity is at its maximum. Striking the F2 key results in a display of a vertical dashed line running from the curve peak to its wavelength on the x-axis. Simultaneously a statement appears in the upper right corner showing the temperature and the wavelength of the maximum intensity.

Stefan-Boltzmann's Law predicts the total intensity output for an object, given its temperature. The total intensity is the summation of the intensities at all the wavelengths. With the area under the curve entirely lit up the viewer sees clearly the portion of light emitted that is at visible wavelengths. One also sees why stars have color. The height of the blue color end of the visible spectrum in relation to the red end will show clearly how these laws explain colors as predominantly a temperature effect.

A Planck diagram is also set up to demonstrate temperatures in the range of 1 to 10 K, appropriate for the cosmic background radiation. The CBR is the greatly redshifted light relic of the expanding, cooling and neutralizing very early (approximately 300,000 year old) plasma universe of the Big Bang. Curves are plotted relative to the peak of the actual CBR curve, with a temperature of 2.735 K. Entering 2.73 to 2.74 K will display the true CBR in red, other curves are plotted in gray.

IBM & compatibles, DOS or Windows (using DOS prompt) $24.95